This invention relates to a phase shifter circuit for use in an electronic musical instrument. More particularly, it relates to a phase shifter circuit which, when used in combination with an electronic musical instrument such as an electronic organ, is suitable to bestow sound effects called the vibrato effect, the chorus effect, the tremolo effect etc. by varying the quantity of phase shift by a voltage.
The phase shifter circuit for bestowing the effects when used in the musical instrument has heretofore been proposed in several forms though small in number. As typical ones, there are known a phase shifter circuit employing an FET and a phase shift modulation system based on the AM modulation.
In case of the phase shifter circuit employing the FET, the characteristics of the FET's to be used have a considerable dispersion, so that the drain-source admittances differ considerably for an identical gate-source voltage. Besides, the drain-source admittance varies abruptly in response to gate-source voltages of a narrow range of about 1.0 V - 1.5 V, so that the phase shift - versus - control voltage characteristic of the phase shifter circuit becomes very indeterminate. In the actual use, it is necessary to adjust the FET's one by one after assembling the circuits or to select FET's of uniform characteristics before the employment. The quantity of linear variable phase shift per stage of FET is considerably small. Where the multistage connection is adopted in order to attain a large quantity of phase shift, an adjustment for making the characteristics of the respective FET's uniform is troublesome. In order to avoid the disadvantages inherent to the FET, there has been further proposed a circuit in which a capacitor and an FET are connected in series with the emitter of a transistor, a capacitor is connected to the collector thereof, and the terminals are connected in common for an output end, or a circuit which employs an operational amplifier. However, the former has the disadvantage that, since the output impedance on the collector side cannot be made very low, the amplitude becomes small at high frequencies. The latter has the disadvantage that the cost becomes high due to the employment of the operational amplifier.
In case of the phase shift modulation system based on the AM modulation, the phase shifter circuit becomes complicated. Besides, since the system itself originally intends the phase modulation by low frequencies, the voltage control by d.c. is difficult to be realized and the band in which the phase modulation is done is narrow.
This invention proposes a voltage-controlled phase shifter circuit for an electronic musical instrument as has eliminated all the disadvantages attendant upon the prior-art phase shifter circuits.